The present invention relates to an ink-jet printing apparatus that is capable of obtaining printed materials that are free of occurrence of color migration and have good appearance even when printed on a resin printing medium using a water-based ink, and an ink-jet printing method. The present invention provides an ink-jet printing apparatus including an ink-jet printing head that ejects a water-based ink onto a resin printing medium that is transported in a feeding direction thereof, and an under heater that heats the printing medium from a rear side surface of the printing medium opposed to a front side surface thereof which faces to the ink-jet printing head, in which the under heater is disposed at a position spaced at a distance of from 0.05 to 3.0 mm apart from the rear side surface of the printing medium upon printing, and an ink-jet printing method using the ink-jet printing apparatus.